iPhone 4's screen is turning black randomly

I'm getting a black screen randomly in my iPhone 4. After I put the phone on sleep, when I click the switch button to wake the phone, it'll just light with a black screen. I need to click the switch button many times on and off to get the display working on the screen.

It also use to happen when the phone on sleep and receive call, the phone will ring but I can't see anything on the screen even though I can still answer the call by sliding where I suppose to slide usually, which means the screen is working and all the buttons are active but they're not displaying.

I confirmed this as a hardware problem because this problem started with me since I was on 4.2.1 and I restored the phone through 4.3 and 4.3.1 and the problem still exist. Moreover, the problem also appears when the phone was out of buttery and off, where you switch on the phone and it shows you that empty buttery with a lightning. Based on that I believe it's a hardware problem.

But I don't know what are the causes and what is the solution if there's any?!